Synthesis and characterization of the monomeric vicinal dianion Li 2(THF)3[ArNC(SiMe3)2] and the aluminum and lithium derivatives of the amido ligand [ArNCH(SiMe 3)2]_

Article abstract of DOI:10.1021/om700972a

Reaction of the imine ArNC(SiMe₃)₂ (1; Ar = 2,6-iPr₂C₆H₃) with LiAlH₄ in THF resulted in the formation of the dimeric hydroaluminate [(THF) ₂LiH₃AlL]₂ (2; L = [ArNCH(SiMe ₃)₂]^-). 2 reacted with CH₃I to give the monomeric aluminum dihydride LAlH₂(THF) (3), which can be converted to the diiodide LAlI₂(THF) (4) upon treatment with 2 equiv of Me₃SiI. The quasi two-coordinate lithium amide Li(OEt ₂)L (8) with an intramolecular CH-Li interaction was obtained by the deprotonation of the corresponding amine LH (5) generated from hydrolysis of 2. Reduction of 1 with lithium in THF resulted in the first structurally characterized monomeric C-N vicinal dianion, Li₂(THF) ₃[ArNC(SiMe₃)₂] (6), and the monomeric lithium amide Li(THF)₂L (7).

Full text of DOI:10.1021/om700972a

678
Organometallics 2008, 27, 678–682
Synthesis and Characterization of the Monomeric Vicinal Dianion
Li2(THF)3[ArNC(SiMe3)2] and the Aluminum and Lithium
Derivatives of the Amido Ligand [ArNCH(SiMe3)2]-
Xiaoyan Cheng, Jianying Zhang, Haibin Song, and Chunming Cui*
State Key Laboratory and Institute of Element-Organic Chemistry, Nankai UniVersity,
Tianjin 300071, People’s Republic of China
ReceiVed September 30, 2007
Reaction of the imine ArNC(SiMe3)2 (1; Ar ) 2,6-iPr2C6H3) with LiAlH4 in THF resulted in the
formation of the dimeric hydroaluminate [(THF)2LiH3AlL]2 (2; L ) [ArNCH(SiMe3)2]-). 2 reacted with
CH3I to give the monomeric aluminum dihydride LAlH2(THF) (3), which can be converted to the diiodide
LAlI2(THF) (4) upon treatment with 2 equiv of Me3SiI. The quasi two-coordinate lithium amide Li(OEt2)L
(8) with an intramolecular CH-Li interaction was obtained by the deprotonation of the corresponding
amine LH (5) generated from hydrolysis of 2. Reduction of 1 with lithium in THF resulted in the first
structurally characterized monomeric C-N vicinal dianion, Li2(THF)3[ArNC(SiMe3)2] (6), and the
monomeric lithium amide Li(THF)2L (7).
Scheme 1
Introduction
Reduction of imines by active metals or low-valent metal
complexes constitutes a powerful method for the synthesis of
vicinal diamines and R-amino alcohols via their homocoupling
and cross-coupling reactions.1 Earlier studies have shown that
reduction of imines by alkali metals generated various products,
among which the corresponding radical anions and vicinal
dianions are the key intermediates.2 Despite the fundamental
importance of these highly reactive intermediates, detailed
structural studies of these intermediates have not been achieved,
owing to their high reactivity and tendency to form large
aggregates in both solution and the solid state.
There has been considerable interest in the synthesis and
structural characterization of organolithium species, since they
are versatile nucleophiles and ligand transfer reagents in organic
and organometallic synthesis.3 Bulky amide ligands are par-
ticularly attractive because of their unusual kinetic stabilizing
ability for unusual oxidation state, low-coordinate, and highly
reactive metal complexes.4 Imines with different substituents
are readily available and are thus excellent precursors for the
preparation of various secondary amines, which can be subse-
quently converted to lithium amides by deprotonation. Lithium
aluminum hydride has been frequently used for the reduction
of imines to generate the corresponding amines. The hydroalu-
minate intermediates may be isolated and fully characterized
when imines with bulky substituents are employed.5 Herein we
report on the reduction of the bulky imine ArNC(SiMe3)2 (1;
Ar ) 2,6-iPr2C6H3)6 with lithium aluminum hydride and lithium
and the subsequent isolation and crystal structures of a trihy-
droaluminate, a monomeric vicinal dianion, and a monomeric
lithium amide with an intramolecular CH-Li interaction.
Results and Discussion
* To whom correspondence should be addressed. E-mail: cmcui@
nankai.edu.cn.
The reaction of ArNC(SiMe3)2 (1; Ar ) 2,6-iPr2C6H3) with
LiAlH4 in refuxing THF afforded the hydroaluminate [(THF)2-
LiH3AlL]2 (2; L ) [ArNCH(SiMe3)2]-) (Scheme 1). Crystals
of 2 could be obtained from toluene at low temperature. The
X-ray crystal structure of 2 (Figure 1) disclosed that 2 is a dimer
with a hydride-bridged eight-membered ring. The structure is
similar to those of several structurally characterized trihydroalu-
(1) For examples: (a) Roskamp, E. J.; Pederson, S. F. J. Am. Chem.
Soc. 1987, 109, 6551. (b) Jones, D. S.; Srinivasan, A.; Kasina, S.; Fritzgerg,
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Y.; Zhang, Y. Synth. Commun. 1997, 27, 1483. (d) Talukdar, S.; Banerji,
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Fujiwara, Y. J. Org. Chem. 2001, 66, 514. (f) Kim, M.; Knettle, B. W.;
Dahlen, A.; Himersson, G.; Flowers, R. A., II Tetrahedron 2003, 59, 10397.
(2) (a) Smith, J. G.; Turle, R. A. J. Org. Chem. 1972, 40, 495. (b) Smith,
J. G.; Ho, I.; Simpson, G. E. F. J. Org. Chem. 1975, 40, 495. (c) Smith,
J. G.; Simpson, G. E. F. J. Org. Chem. 1976, 41, 2878. (d) Smith, J. G.;
Mitchell, D. G. J. Am. Chem. Soc. 1977, 99, 5045.
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and Metalloid Amides: Physical Properties and Structures; Ellis Horwood-
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10.1021/om700972a CCC: $40.75
2008 American Chemical Society
Publication on Web 01/31/2008

Monomeric Vicinal Dianion Li2(THF)3[ArNC(SiMe3)2]
Organometallics, Vol. 27, No. 4, 2008 679
Figure 1. Ortep drawing of 2 with 30% probability ellipsoids.
Selected bond lengths (Å) and angles (deg): Al1-N1 ) 1.8473(16),
Li1-O1 ) 1.927(4), Li1-O2 ) 1.916(4), Al1-H1d ) 1.53(3),
Al1-H1e ) 1.58(3); O1-Li1-O2 ) 107.86(18).
Figure 2. Ortep drawing of 3 with 30% probability ellipsoids.
Selected bond lengths (Å) and angles (deg): N1-Al1 ) 1.8251(13),
O1-Al1 ) 1.9404(13), N1-C1 ) 1.4334(18), N1-C13 )
1.5161(17), Al1-H1 ) 1.518(17), Al1-H2 ) 1.50(2); N1-Al1-O1
) 114.89(5).
minates stabilized by bulky ligands.7 Treatment of 2 with neat
MeI in toluene yielded the neutral aluminum dihydride
LAlH2(THF) (3) in good yield.8 Attempts to remove the
coordinated THF molecule in 3 at elevated temperatures were
unsuccessful, due to its low thermal stability. The structure of
3 is shown in Figure 2 along with selected bond parameters. 3
is a monomer, and the central aluminum atom adopts a distorted-
tetrahedral geometry. Treatment of 3 with 2 equiv of Me3SiI
gave the expected aluminum diiodide LAlI2(THF) (4) in
excellent yield. Crystals of 4 from n-hexane at 4 °C are suitable
for X-ray investigation, and the results of a structural analysis
are presented in Figure 3. 4 is a monomer, and the molecular
geometry is very similar to that of 3 (Figure 3). The aluminum
atom, bound to two iodide ligands, a THF donor, and a bulky
amido ligand, is four-coordinate. The Al-N bond length
(1.8063(19) Å) of
4 is slightly longer than that in
(Ar(SiMe3)NAlI2)2(1.784(6) Å).9 The Al-I bond lengths
(2.5418(7) and 2.5710(7) Å) in 4 are comparable to those
observed in the reported alumiunm diiodides.10
Reduction of the imine 1 with an excess of lithium in dry
THF at room temperature for 6 h yielded a deep red solution,
from which dark red crystals of 6 were isolated. Similar
reduction with 1 equiv of lithium gave 7 as orange crystals in
modest yield. 7 was presumably formed via the abstraction of
a hydrogen atom from the solvent by the highly reactive radical
anion [ArNC(SiMe3)2]– Reaction of 1 with LiAlH4 in refluxing
THF followed by hydrolysis yielded the amine 5, which can be
deprotonated in THF and diethyl ether to give 7 and 8,
Figure 3. Ortep drawing of 4 with 30% probability ellipsoids.
Selected bond lengths (Å) and angles (deg): Al1-N1 ) 1.8063(19),
Al1-O1 ) 1.8682(16), Al1-I1 ) 2.5418(7), Al1-I2 ) 2.5710(7),
N1-C9 ) 1.452(3), N1-C13 ) 1.530(3); N1-Al1-O1 )
106.13(8), N1-Al1-I1 ) 119.37(7), O1-Al1-I1 ) 104.10(6),
N1-Al1-I2 ) 124.28(7), O1-Al1-I2 ) 95.30(6), I1-Al1-I2
) 103.33(3).
(7) (a) Wehmschulte, R. J.; Ellison, J. J.; Ruhlandt-Senge, K.; Power,
P. P. Inorg. Chem. 1994, 33, 6300. (b) Eaborn, C.; Gorrell, I. B.; Hitchcock,
P. B.; Smith, J. D.; Tavakkoli, K. Organometallics 1994, 13, 4143. (c) Heine,
A.; Stalke, D. Angew. Chem., Int. Ed. Engl. 1992, 31, 854. (d) Wehmschulte,
R. J.; Grigsby, W. J.; Schiemenz, B.; Bartlett, R. A.; Power, P. P. Inorg.
Chem. 1996, 35, 6694.
respectively, in high yield (Scheme 2). All of the lithium salts
are extremely air and moisture sensitive.
1
The H and 13C NMR spectra of 6 only show two broad
(8) (a) Wehmschulte, R. J.; Power, P. P. Inorg. Chem. 1994, 33, 5611.
(b) Wehmschulte, R. J.; Power, P. P. Inorg. Chem. 1996, 35, 3262.
(9) Schiefer, M.; Reddy, N. D.; Roesky, H. W.; Vidovic, D. Organo-
metallics 2003, 22, 3637.
resonances for the three coordinated THF molecules, indicating
rapid exchange of the two lithium ions on the NMR time scale
at ambient temperature. Thus, the 7Li NMR spectrum displays
one signal, appearing at -1.40 ppm. The 13C signal of the
anionic carbon is observed at 5.80 ppm, which is a marked shift
(10) (a) Zhao, J.; Song, H.; Cui, C. Organometallics 2007, 26, 1947.
(b) Stender, M.; Eichter, B. E.; Hardman, N. J.; Power, P. P.; Prust, J.;
Noltemeyer, M.; Roesky, H. W. Inorg. Chem. 2001, 40, 2794.

680 Organometallics, Vol. 27, No. 4, 2008
Cheng et al.
Scheme 2
to upper field relative to that of 1 (ca. δ 218 ppm) due to the
location of the negative charge.6 The 29Si NMR resonance of
the trimethylsilyl groups also appeared at high field (δ -15.7
ppm). The molecular structure of 6 was finally confirmed by
X-ray single-crystal analysis.
Single crystals of 6 suitable for X-ray analysis were obtained
from THF at -40 °C, and crystallographic analysis revealed a
monomeric structure (Figure 4). The most notable structural
feature is that the Li2 ion is coordinated to both the central C1
and N1 atoms with the formation of the unique lithiaazacyclo-
propane structure, while the Li1 ion is coordinated to the N1
atom. Both the lithium ions are three-coordinate with the normal
Li2-C1 bond length of 2.072(5) Å and Li-N distances of
1.907(5) and 1.908(5) Å.11 The Li1-Li2 separation is 2.637
Å. The C1-Li2-N1 angle (44.86(16)°) is acute. The C1-N1
bond length (1.526(4) Å) is significantly longer than those found
in structurally characterized transition-metal η2-imine complexes
(1.41–1.45 Å),12 indicating the strong vicinal dianonic character
of 6. The geometry around the C1 atom is almost planar (mean
derivation from the plane 0.0381 Å), while that of the N1 atom
is pyramidal.
Figure 4. Ortep drawing of 6 with 30% probability ellipsoids.
Selected bond lengths (Å) and angles (deg): Li1-N1 ) 1.908(5),
Li1-O1 ) 1.907(6), Li1-O2 ) 2.024(4), C1-Li2 ) 2.072(5),
N1-Li2 ) 1.907(5), Li2-O3 ) 1.957(5), C1-N1 ) 1.526(4);
C1-N1-Li2 ) 73.3(2), N1-C1-Li2 ) 61.8(2), N1-Li2-C1 )
44.86(16), Si1-C1-Si2 ) 120.58(19).
Although the dianion species (Ph2CNPh)2- is known and has
served as a model compound in studying the chemical behavior
of such anions, the isolation and structural characterization of
this type of alkali-metal species has not been realized to date.2
It is noted that a handful of metal η2-imine complexes, including
those of calcium and lanthanides, have been structurally
characterized.12 To the best of our knowledge, compound 6
represents the first well-characterized vicinal dianion generated
by reduction of an imine with alkali metals.
1
7
The lithium amides 7 and 8 were characterized by H, Li,
13C, and 29Si NMR spectroscopy. The 1H NMR spectrum of 7
indicates that two THF molecules are coordinated to the lithium
ion. The lithium resonance in the 7Li NMR spectrum of 7
appears at -2.25 ppm. The spectroscopic data support the
monomeric lithium amide structure with the three-coordinate
1
lithium atom. The H NMR spectrum of 8 disclosed that only
Figure 5. Ortep drawing of 8 with 30% probability ellipsoids.
Selected bond lengths (Å) and angles (deg): N1-C1 ) 1.3956(18),
N1-Li1 ) 1.853(3), N1-C13 ) 1.4999(18), Li1-O1 ) 1.900(3),
Si2-C17 ) 1.8836(17); C1-N1-C13 ) 118.88(12), C1-N1-Li1
) 115.11(13), C13-N1-Li1 ) 125.65(13), N1-Li1-O1 )
152.08(19).
one diethyl ether molecule is solvated. In order to disclose the
coordination environment of the lithium ion, an X-ray single-
crystal analysis was carried out.
Single crystals of 8 were obtained from n-hexane at -25 °C.
The structure is shown in Figure 5, along with selected bond
parameters. Compound 8 is monomeric, with a formally two-
coordinate lithium ion. It is noted that two-coordinated lithium
ions have been found in dimeric and oligomeic lithium amides.13
The Li-N bond length (1.853(3) Å) is relatively shorter
compared to those found in the known monomeric lithium
amides, due to the low-coordinate lithium atom of 8. There are
only a few structurally characterized monomeric lithium amides,
(11) (a) Olsher, U.; Izatt, R. M.; Bradshaw, J. S.; Dalley, N. K. Chem.
ReV. 1991, 91, 137. (b) Sekiguchi, A.; Nakanishi, T.; Kabuto, C.; Sakurai,
H. J. Am. Chem. Soc. 1989, 111, 3748. (c) Ebata, K.; Setaka, W.; Inoue,
T.; Kabuto, C.; Kira, M.; Sakurai, H. J. Am. Chem. Soc. 1998, 120, 1335.
(12) Examples: (a) Cameron, T. M.; Ortiz, C. G.; Abboud, K. A.;
Boncella, J. M.; Baker, R. T.; Scott, B. L. Chem. Commun. 2000, 573. (b)
Hou, Z.; Yoda, C.; Koizumi, T.; Nishiura, M.; Wakatsuki, Y.; Fukuzawa,
S.; Takats, J. Organometallics 2003, 22, 3586. (c) Takai, K.; Ishiyama, T.;
Yasue, H.; Nobunaka, T.; Itoh, M.; Oshiki, T.; Mashima, K.; Tani, K.
Organometallics 1998, 17, 5128. (d) Makioka, Y.; Taniguchi, Y.; Fujiwara,
Y.; Takaki, K.; Hou, Z.; Wakatsuki, Y. Organometallics 1996, 15, 5476.
(e) Buch, F.; Harder, S. Organometallics 2007, 26, 5132. (f) Takaki, K.;
Komeyama, K.; Takehira, K. Tetrahedron 2003, 59, 10381.
(13) (a) Lappert, M. F.; Slade, M. J.; Singh, A.; Atwood, J. L.; Rogers,
R. D.; Shakir, R. J. Am. Chem. Soc. 1983, 105, 302. (b) Wright, R. J.;
Steiner, J.; Beaini, S.; Poer, P. P. Inorg. Chim. Acta 2006, 359, 1939.

Monomeric Vicinal Dianion Li2(THF)3[ArNC(SiMe3)2]
Organometallics, Vol. 27, No. 4, 2008 681
Synthesis of LAlI2(THF) (4). To a solution of 3 (0.44 g, 1.0
mmol) in toluene was added Me3SiI (0.28 mL, 2.0 mmol) at room
temperature. The mixture was then stirred at room temperature for
12 h. The solvent was removed under vacuum, and the remaining
white solid was recrystallized from n-hexane at 4 °C to give
colorless crystals of 4 (0.62 g, 90%). Mp: 126–128 °C dec. 1H
NMR (400 MHz, C6D6): δ 6.94–7.02 (m, 3H, Ar H), 4.03 (sept, J
) 6.4 Hz, 2H, CHMe2), 3.42 (br s, 4H, OCH2), 3.27 (s, 1H,
CH(SiMe3)2), 1.37 (d, J ) 6.4 Hz, 6H, CHMe2), 1.29 (d, J ) 6.4
Hz, 6H, CHMe2), 0.84 (br s, 4H, OCH2CH2), 0.34 (s, 18H, SiMe3).
13C NMR (400 MHz, C6D6): δ 150.18, 149.42, 126.50, 125.10 (Ar
C), 75.34 (OCH2), 47.12 (CH(SiMe3)2), 28.13, 26.67 (CHMe2),
25.53 (OCH2CH2), 24.39 (CHMe2), 4.98 (SiMe3).
Synthesis of Li2(THF)3[ArNC(SiMe3)2] (6). A solution of imine
1 (1.77 g, 5.0 mmol) in THF (50 mL) was added to finely divided
lithium turnings (0.074 g, 10.5 mmol) at room temperature. After
the mixture was stirred for 6 h, all volatiles were removed. The
remaining brown-red solid was recrystallized from THF at -40
°C to give dark red crystals of 6 (1.7 g, 60%). Mp: 109 °C dec. 1H
NMR (400 MHz, C6D6): δ 6.69–7.20 (m, 3H, Ar H), 4.75 (sept, J
) 6.80 Hz, 2H, CHMe2), 3.32 (br s, 12H, OCH2), 1.41 (d, J )
6.80 Hz, 12H, CHMe2), 1.27 (br s, 12H, OCH2CH2), 0.42 (s, 18H,
SiMe3). 13C NMR (125.8 MHz, C6D6): δ 158.6, 139.5, 123.7, 111.4
(Ar C), 70.2, 70.0 (OCH2), 48.2 (CHMe2), 26.2 (OCH2CH2), 25.7,
25.6 (CHMe2), 5.8 (C(SiMe3)2), 0.87 (SiMe3). 7Li NMR (116.6
MHz, C6D6): δ -1.40. 29Si NMR (59.6 MHz, C6D6, TMS): δ
-15.73. UV/vis (hexane): λmax (nm) 215, 244. UV/vis (THF): λmax
(nm) 247, 253, 259.
Synthesis of Li(THF)2L (7). This compound was prepared by
the reduction of the imine 1 with 1 equiv of lithium (yield 50%) in
THF or deprotonation of 5 with n-BuLi in THF at room temperature
(yield 90%). Mp: 122 °C dec. 1H NMR (400 MHz, C6D6): δ
6.76–7.15 (m, 3H, Ar H), 4.21 (sept, J ) 6.80 Hz, 1H, CHMe2),
3.62 (sept, J ) 6.80 Hz, 1H, CHMe2), 3.33 (br s, 8H, OCH2), 3.29
(s, 1H, CH(SiMe3)2), 1.50 (d, J ) 6.80 Hz, 6H, CHMe2), 1.31 (d,
J ) 6.80 Hz, 6H, CHMe2), 1.23 (br s, 8H, OCH2CH2), 0.27 (s,
18H, SiMe3). 13C NMR (125.8 MHz, C6D6): δ 134.4, 125.9, 123.0,
112.5 (Ar C), 68.5 (OCH2), 46.2 (CH(SiMe3)2), 29.0 (CHMe2), 26.0
(CHMe2), 25.9 (CHMe2), 25.8 (CHMe2), 25.3 (OCH2CH2), 0.71
(SiMe3). 7Li NMR (116.6 MHz, C6D6, 1 M LiCl in D2O): δ -2.25.
29Si NMR (59.6 MHz, C6D6): δ 4.02.
in which the lithium ions are three- and four-coordinate with
Li-N bond lengths ranging from 1.895 to 1.957 Å.14 The
geometry of the N1 atom is almost planar (mean derivation from
the plane 0.0200 Å). The most striking feature of 8 is the close
Li1-C17 interaction (2.511 Å) due to the coordination unsat-
uration of the lithium ion. This kind of interaction is not common
for solvated alkali-metal species. However, it has been observed
in bulky silyl- and germyllithium and alkyllithium species.15
In conclusion, hydroalumination of the bulky imine 1 yielded
the well-defined hydroaluminate 2, which could be easily
converted to the neutral aluminum dihydride and diiodide 3 and
4. The monomeric vicinal dianionic species 6 has been isolated
and structurally characterized. The lithium amide 8 is a monomer
with the shortest Li-N bond length observed in the solid state.
These results indicate that the bulky amido ligand L could
support monomeric metal complexes.
Experimental Section
General Remarks. All operations were carried out under an
atmosphere of dry argon or nitrogen by using modified Schlenk
line and glovebox techniques. All solvents were freshly distilled
from Na and degassed immediately before use. The chemicals used
in this study were purchased from Aldrich and Acros and used as
received. ArNC(SiMe3)2 (Ar ) 2,6-iPrC6H3) was prepared as
described in the literature.6 The 1H, 7Li, 13C, and 29Si NMR
spectroscopic data were recorded on Varian Mercury Plus 300, 400,
and 600 M NMR spectrometers.
Synthesis of [(THF)2LiH3AlL]2 (2). A solution of imine 1 (1.765
g, 5.0 mmol) in THF was added to LiAlH4 (0.209 g, 5.5 mmol) in
THF at room temperature. The mixture was refluxed for 10 h. The
solvent was removed under vacuum, and the remaining yellow-
white solid was washed with n-hexane and recrystallized from
toluene at -40 °C to give colorless crystals of 2 (1.80 g, 70%).
Mp: 147–149 °C dec. 1H NMR (400 MHz, C6D6): δ 7.07–7.10
(m, 3H, Ar H), 4.07 (sept, J ) 6.8 Hz, 2H, CHMe2), 3.47 (t, J )
6.0 Hz, 8H, OCH2), 2.59 (s, 1H, CH(SiMe3)2), 1.52 (d, J ) 6.8
Hz, 6H, CHMe2), 1.38 (m, J ) 6.0 Hz, 8H, OCH2CH2), 1.30 (d, J
) 6.8 Hz, 6H, CHMe2), 0.44 (s, 18H, SiMe3). 13C NMR (400 MHz,
C6D6): δ 157.22, 146.28, 124.22, 121.58 (Ar C), 68.40 (OCH2),
50.77 (CH(SiMe3)2), 27.72, 27.62 (CH(CH3)2), 25.54 (OCH2CH2),
24.56 (CH(Me3)2), 2.79 (SiMe3).
Synthesis of Li(OEt2)L (8). A solution of n-BuLi (2.5 mL, 2.5
M in n-hexane) was added to a solution of 5 (0.34 g, 1.0 mmol) in
Et2O (40 mL) at room temperature. The mixture was stirred at room
temperature for 15 h. The solvent was removed under vacuum to
afford a yellow powder, which was recrystallized from n-hexane
at -25 °C to give yellow crystals of 8 (0.39 g, 95%). Mp: 53-55
Synthesis of LAlH2(THF) (3). To a solution of 2 (0.52 g, 1.0
mmol) in toluene was added CH3I (0.06 mL, 1.2 mmol) at room
temperature. The mixture was then stirred at room temperature for
12 h. The solvent was removed under vacuum, and the remaining
yellow-white solid was recrystallized from toluene to give colorless
1
°C. H NMR (400 MHz, C6D6): δ 6.80–7.12 (m, 3H, Ar H), 3.97
1
(br s, 1H, CHMe2), 3.65 (br s, 1H, CHMe2), 3.19 (s, 1H,
CH(SiMe3)2), 2.74 (q, J ) 7.20 Hz, 4H, OCH2), 1.43 (d, J ) 4.40
Hz, 6H, CHMe2), 1.26 (d, J ) 4.40 Hz, 6H, CHMe2), 0.66 (t, J )
7.2 Hz, 6H, OCH2CH3), 0.21 (s, 18H, SiMe3). 13C NMR (400 MHz,
C6D6): δ 156.8, 125.7, 123.0, 114.0 (Ar C), 66.3 (OCH2), 45.0
(CH(SiMe3)2), 28.8 (CHMe2), 26.7 (CHMe2), 25.6 (CHMe2), 25.3
(CHMe2), 14.2 (OCH2CH3), 0.59 (SiMe3). 7Li NMR (116.6 MHz,
C6D5-CD3): δ -1.80. 29Si NMR (59.6 MHz, C6D5-CD3): δ
-3.53.
crystals of 3 (0.32 g, 73%). Mp: 100–102 °C dec. H NMR (300
MHz, C6D6): δ 7.0–7.15 (m, 3H, Ar H), 4.0 (sept, J ) 6.6 Hz, 2H,
CHMe2), 3.46 (t, J ) 6.3 Hz, OCH2), 2.65 (s, 1H, CH(SiMe3)2),
1.51 (d, J ) 6.6 Hz, 6H, CHMe2), 1.28 (d, J ) 6.6 Hz, 6H, CHMe2),
0.92 (m, J ) 6.3 Hz, OCH2CH2), 0.40 (s, 18H, SiMe3) ppm. 13C
NMR (300 MHz, C6D6): δ 153.35, 145.42, 125.11, 122.85 (Ar C),
71.84 (OCH2), 50.15 (CH(SiMe3)2), 27.80, 27.02 (CHMe2), 25.41
(OCH2CH2), 24.61 (CHMe2), 2.42 (SiMe3).
X-ray Structure Determination. Data were collected on a
Bruker Smart-Apex II diffractometer using graphite-monochromated
Mo KR (λ ) 0.710 70 Å) radiation. All structures were solved by
direct methods (SHELXS-97)16 and refined by full-matrix least
squares on F2. All non-hydrogen atoms were refined anisotropically,
and hydrogen atoms were refined by a riding model (SHELXL-
(14) (a) Grotjahn, D. B.; Sheridan, P. M.; Jihad, I. A.; Ziurys, L. M.
J. Am. Chem. Soc. 2001, 123, 5489. (b) Chen, H.; Bartlett, R. A.; Dias,
H. V. R.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1989, 111,
4338. (c) Fjeldberg, T.; Hitchcock, P. B.; Lappert, M. F.; Thorne, A. J.
J. Chem. Soc., Chem. Commun. 1984, 822. (d) Clegg, W.; Liddle, S. T.;
Mulvey, R. E.; Robertson, A. J. Chem. Soc., Chem. Commun. 1999, 511.
(e) Andrews, P. C.; Duggan, P. J.; Fallon, G. D.; McCarthy, T. D.; Peatt,
A. C. Dalton Trans. 2000, 1937.
(15) (a) Nakamoto, M.; Fukawa, T.; Lee, V. Ya.; Sekiguchi, A. J. Am.
Chem. Soc. 2002, 124, 15160. (b) Siemeling, U.; Redecker, T.; Neumann,
B.; Stammler, H.-G. J. Am. Chem. Soc. 1994, 116, 5507. (c) Sapse, A.-M.;
Schleyer, P. v. R. Lithium Chemistry: A Theoretical and Experimental
OVerView; Wiley: New York, 1995.
(16) (a) Sheldrick, G. M. SHELXS-90/96, Program for Structure Solution.
Acta Crystallogr., Sect. A 1990, 46, 467. (b) Sheldrick, G. M. SHELXL-
97, Program for Crystal Structure Refinement; University of Gottingen,
Gottingen, Germany, 1997.

682 Organometallics, Vol. 27, No. 4, 2008
Cheng et al.
97).16 Crystallographic data for 2: T ) 113(2) K, monoclinic, space
group P21/n, a ) 13.225(2) Å, b ) 17.355(3) Å, c ) 14.270(3) Å,
ꢀ ) 95.577(2)°, V ) 3259.7(10) Å3, Z ) 4, R1 ) 0.0483, wR2 )
0.1312 for 7782 independent reflections; R1 ) 0.0689, wR2 )
0.1392 for all data. Crystallographic data for 3: T ) 113(2) K,
monoclinic, space group P21, a ) 9.447(2) Å, b ) 12.565(3) Å, c
) 11.380(3) Å, ꢀ ) 91.994(4)°, V ) 1349.9(6) Å3, Z ) 2, R1 )
0.0323, wR2 ) 0.0690 for 6853 independent reflections; R1 )
0.0398, wR2 ) 0.0724 for all data. Crystallographic data for 4: T
) 113(2) K, monoclinic, space group P21/c, a ) 10.4567(6) Å, b
) 14.0978(8) Å, c ) 20.6210(14) Å, ꢀ ) 99.981(3)°, V ) 2993.9(3)
Å3, Z ) 4, R1 ) 0.0386, wR2 ) 0.0636 for 7136 independent
reflections; R1 )0.0341, wR2 ) 0.0662 for all data. Crystal-
lographic data for 6: T ) 173(2) K, monoclinic, space group P21,
a ) 10.134(4) Å, b ) 17.794(7) Å, c ) 10.376(4) Å, ꢀ )
112.011(6)°, Z ) 2, R1 ) 0.0763, wR2 ) 0.1093 for 6818
independent reflections; R1 ) 0.0764, wR2 ) 0.1192 for all data.
Crystallographic data for 8: T ) 113(2) K, monoclinic, space group
P21/n, a ) 9.9324(12) Å, b ) 17.397(2) Å, c ) 16.0983(18) Å, ꢀ
) 101.203(2)°. V ) 2728.7(5) Å3, Z ) 4, R1 ) 0.0483, wR2 )
0.1104 for 6488 independent reflections; R1 ) 0.0658, wR2 )
0.1179 for all data.
Acknowledgment. This work was supported by the
National Natural Science Foundation of China (NSFC) and
the NCET.
Supporting Information Available: CIF files for the structures
of 2-4, 6, and 8. This material is available free at charge at the
Internet at http://pubs.acs.org.
OM700972A